When working with liquids, it is often desirable to divide a single stream of liquid into several smaller, equal streams of liquid. This is typically done using a fluid metering device such as liquid flow divider, an equal-flow pump, or an equal-flow liquid motor.
A typical prior art liquid flow divider is taught in U.S. Pat. No. 4,531,535 to Kiernan (“Kiernan”). As shown in FIG. 4 of Kiernan, such liquid flow dividers typically include multiple dividing units of two intermeshed spur gears. The various dividing units are typically linked together by a drive train that may include a drive line, drive shafts, or a sun gear. As a result of this linkage, all of the gears within the various dividing units rotate at substantially the same speed.
Within each individual dividing unit, a liquid inlet port is positioned on one side of the intermeshing portion of the pair of spur gears, and a liquid discharge port is positioned on the other side of the intermeshing portion of the pair of spur gears. A housing is provided that conforms to the exterior portions of the spur gears that are not in communication with the liquid inlet port or the liquid discharge port. All of the various dividing units' liquid inlet ports are in communication with a single, pressurized liquid source.
In operation, pressurized liquid from the pressurized liquid source first enters each dividing unit's liquid inlet port. The pressurized liquid then causes the gears in each dividing unit to rotate in opposite directions so that each gear's gear teeth carry liquid from the liquid inlet port, around the exterior portion of the gear, and into the liquid discharge port. Because all of the dividing gears within the liquid flow divider are preferably the same size and shape, and because the gears are linked together by a central drive train so that all of the gears rotate at the same rate, the flow rate of liquid around each of the flow divider's various gears is identical to the flow rate of liquid around each of the flow divider's other gears. Accordingly, because each dividing unit includes two gears that convey liquid from the dividing unit's liquid inlet port to the dividing unit's liquid discharge port, liquid flows through each dividing unit at a rate that is equal to two times the rate at which the liquid flows around a single gear.
Accordingly, prior art liquid flow dividers are typically designed to include one dividing unit for each equal discharge stream that the flow divider is to produce. For example, if the flow divider is to produce 10 equal discharge streams of liquid, the flow divider will include 10 separate dividing units. As noted above, these dividing units are linked together by a drive train, such as a drive line or a central sun gear.
Such prior art liquid flow dividers have significant disadvantages. First, because it is necessary to include a separate dividing unit for each discharge stream, these liquid flow dividers tend to be mechanically complex. As a result, the flow dividers tend to be expensive to produce and maintain. Also, because the drive trains within these flow dividers are typically less robust than the other components within the flow dividers, the drive trains often break or otherwise malfunction.
More recent prior art flow dividers, such as the liquid flow divider taught in European Patent Application EP 0 843 097 A1, which was filed on behalf of Pumpenfabrik Ernst Scherzinger (“Scherzinger”) are similar to the flow dividers described above, except that these flow dividers include a planetary gear arrangement within each dividing unit. These planetary gear arrangements include a large central gear, and two to four planetary gears. Each planetary gear intermeshes with the large central gear, and the various planetary gears are spaced equally apart around the perimeter of the central gear. An inlet port and a discharge port are positioned on opposite sides of the intermeshing portion of the central gear and each planetary gear as described above. Accordingly, each planetary gear cooperates with the central gear to produce a single flow element. Thus, Scherzinger teaches using a planetary gear arrangement to provide multiple two-gear flow elements within a single dividing unit. The central gear acts as one of the gears within each two-gear flow element.
The advantage of the liquid flow divider design taught in Scherzinger is that it reduces the number of parts needed to produce a particular number of discharge streams. However, because only a limited number of planetary gears may be positioned around each central gear, such flow dividers typically include an extended array of dividing units that are linked together, or “stacked”, via a drive train as discussed above. Accordingly, like the Kiernan two-gear flow divider, these planetary flow dividers tend to be mechanically complex, which causes the flow dividers to be expensive to produce and maintain. Also, because the drive trains within these flow dividers are typically less robust than the flow divider's other components, the drive trains often break or otherwise malfunction.
A further disadvantage of both the Kiernan and Scherzinger flow dividers is that the design of these flow dividers tends to result in substantial bearing loads being exerted on the bearings that support the flow dividers' various gears. This is due to the fact that liquid flowing through the flow dividers' liquid inlet and discharge ports tends to exert lateral forces on only one side of each gear. This can result in premature failure of the bearings within the flow dividers.
Accordingly, there is a need for improved liquid flow dividers, and other fluid metering devices, that are more robust and that have fewer moving parts than prior art fluid metering devices.